Adjustable pitch propeller



March 3, 1942.

E. H. GODFREY I ADJUSTABLE PITCH PROPELLER Filed March 6, 1957 4 Sheets-Sheet 1 4 k In I l A I I 1 7 re V 3. x g

4 i I l 33 INVENTOR: 38 N Edwmfiodfrg 39 f ATTORNEY TORQUE OR TWISTING MOMENT OF BLADE, LBS.

March 3, 1942.

E. H. GODFREY ADJUSTABLE PITCH PROPELLER Filed March 6, 1937 29 N CD 8 g RADIUS 7 Us A SPRING 28.9ILB5 Q. I. l o 402.86 400 Q} I b 9 g Q 9 L 0 vi d/ (3 W GEAR RATIO 7-ILO-l A HELIX AN6LE=45-P1TCH DIAM.=2.000WEI6HT TRAVELS OUTWARD .lzalT'FoR EACH oNE DEGREE IN BLADE ANGLE o \0 l2 l4 l6 \6 2o 22 DEGREE BLADE ANGLE 12 24 36 48 %2 4 4125 DEGREES GEAR SHAFT MOVEMENT sec 4.00 I

N 6 83 3.875 1 47 9o LIJ i, Q; m u. 520 3.750--5 sk E E W m m 3.625--g D E 1;

' 2 m E 480 3.500 46 7 Q I! Z: 2 3375- a E 440 3.250

A GEAR RATIO 6'-T0-l 3.125 4s-7o '5 \XA g- 400 3.00 s

NVENTOR. I a BLApE 10' ANGLE L2 IN I I4- DEGREES 16 I f so so '10 a0 I00 fifivulm. 5 9- MILES PER HOUR T Y,

March 3, 1942. E. H. GODFREY 2,275,361

ADJUSTABLE PITCH PROPELLER I Filed March 6, 1937 (-4 Sheet-Sheet 3 63 INVENIORI Edwin H. roqfrgy I 47 4Q 64 ATTORNEY.

March 3, 1942. GODFREY I 2,275,361

ADJUSTABLE PITCH PROPELLER Filed March 6; 1937 4 Sheets-Sheet 4 Q 1 BI 80 @9,' I 7a Q 8| I 67 I l l 65A. 1 I9 I' I 1 1 l l l l v v 67 ee :5 8!

INVENTOR: Edwmli'adfrgy ATTORNEY.

' adapted for the work Patented Mar. 3,"1 942 Edwin H. Godfrey,

Wenonah, N. J., assignor, by

meme assignments, to Columbia Aircraft Products, Inc., a corporation of New Jersey Application March 6, 1937, Serial No. 129,487

Claims. (01. 170-162) This invention concerns the automatic control of variable pitch propellers.

A variable pitch propeller of a suitable design is best adapted-in connection "with the craft it is mounted onto perform a predetermined work at a certain pitch or angular setting of the blades. Correspondingly the blades of the said propeller, when angularly set at a higheror lower pitch will in each instance be best adapted to perform a certain work, which is larger or smaller, respectively.

To the work best performed at a certain pitch of a blade corresponds a fixed torque exerted by said blade around its axis of adjustability or variability of pitch. We may counteract that torque by an exactly measured equal reaction. At every other pitch of the blade we have a different torque corresponding to th ideal loadusually ata related speed of rotation of the propeller; and in each instance we may counteract the torque by a predetermined reaction.

It is the object of this invention to provide a simple, sensitive yet rugged mechanism which automatically provides at each different angular setting or pitch of a propeller blade a predetermined reaction exactly equal to and preferably counterbalancing the torque caused at that settling or pitch, when the propeller performs the work for which the said setting or pitch is best adapted.

When and if I obtain the said object, and presuming that the blade isjournalled so that the torque increases with an increase of the angle of day design, and

setting or pitch are not directly correlated, i. e. one is not a simple function of the other. But in the ordinary performance of a craft, say an aeroplane, the preferred pitch at which the propeller' best performs relates to a certain speed of rotation of the propeller. I have carried out exhaustive; tests and computations in connection with a number of variable propellers of present- I have determined that ther exists an almost straight ratio between the angle of the preferred pitch and'the radius extending from the axis of the propeller to the center. of

.. gravity of a weight, when the said radius is adthe pitch, then the working load, and therefore the torque, always tends to return the blade to a lower pitch, and I provide an ideal automatic control of the pitch of the blade of a variable or adjustable propeller, as follows:

As long as the propeller performs the work for which its pitch or setting at that time is best adapted, the reaction completely balances the torque, so that thepitch or setting remains unchanged. -But when the propeller is called upon to perform work in excess of the work for which its pitch or setting at that time is best adapted, then the reactionv is insufficient to balance the increased torque, the blade will be rotated by the increased torque, until a pitch or setting is reached, at whichthe reaction counteracts the torque, andthe new pitch or setting is best now being performed .by the propeller. An opposite adjustment of the pitch under converse conditions is of course readily understood by those familiar with this art.

Now the said torque and the angle of the these and other modifications justed so that the centrifugal force of said weight, at a propeller speed corresponding to the said pitch, is equal to the torque corresponding to the said pitch and therefore also to the desired reaction.

This invention concerns more particularly, in combination with a variable pitch propeller, centrifugal means and a transmission interconnecting the blade of said propeller and said centrifugal means, so that the reaction produced by the centrifugal means is exactly equal to the above referred to torque.

It will be understood from the foregoing, that in accordance with the experiments I have carried out with standard variablepropellers, the radial path of a centrifugally moving weight and the angle of the blade are not exactly correlated.

But within the meaning of-this invention the de- A consideration to a compensation of the said discrepancy, in one or the other of the following ways:

(A) The reaction may be adjusted by variations of weight, e. g. by varying the weight exerting. the centrifugal force.

(B) The actual path of the centrifugal weight may be adjusted, so that its radial path .is in straight-line ratio with the pitch centrifugal force produces the desired reaction.

(C) Adjustment in the transmission by irregular gearing, cam action for instance.

Various additional objects, which attach to of this invention will be better understood from the description of angle, when the v exemplary executions of the invention, as illustrated in the drawings, where- Fig. 1 represents an example for item A, in a cross section normal to the propeller shaft.

Fig. 2 is a chart comparing torque, as it changes with the pitch angle, with centrifugal force changing with the radius, in connection with an arrangement like that of Fig. 1.

Fig. 3 is a quadrant of a cross-sectioned side view illustrating modification B, the line of crosssection being indicated by numeral 3 and arrows in Fig. 3a.

Fig. 3a is a corresponding part end view inside of the housing, the housing being sectioned away. Fig. 4 is another chart, relating to an example falling under the scope of the following figures. Fig. 5 is a sectional cross-sectioned View of the weight and transmission parts concerning a modification under item C. Fig. 6 is a corresponding, sectioned view, looking in the housing onto the inner end of a blade. The actual sectioning is in the plane of the propeller axis, except at and near the stop screws. More particularly the section is ofiset to the back of the propeller shaft at the portion marked 8i3i, so that the propeller shaft does not show in this view.

Fig. 7 is a front elevation of a variable pitch propeller with three blades centrifugally balanced according to this invention.

The propeller of Fig. 1 has a split housing, of which only the rear part H is shown. The detached front part substantially matches in elevation the rear part shown, and is to beassembled therewith by bolts 05 in a plane which substantially coincides with the plane of cross-section of Fig. 1.

Aside from a few parts, such as the key l3 which secures hub i4 arising from the back of the housing upon the propeller shaft l2, the parts to the right and left of a vertical center line, through the axis of the propeller shaft, and above and below a horizontal center linethrough such an axis are substantially symmetrical, at least as far as the broken away parts of the extremities are concerned.

A pair of these extremities are the blades l6 which are encapsuled at their root by rings I! split at IS. Th rings I! together with the blades l6 are journalled in the split bearing ex-' tensions I9 of the housing by way of roller hearing 2| and ball bearings 20.

The capsules 22 of the centrifugal units extend from the housing rectangularly between the propeller blades. The capsules 22 extend through necks 23 provided upon opposite sides of the housing into a bore 24 upon the inside of the housing. Into that bore 24 of the housing fit flanges 25 at the ends of capsules 22. Nuts 2'! are engaged upon the outer circumferences of the capsules 22 and serve to clamp the capsules upon the necks 23. Pins 26 angularly retain the capsules in the necks 23. The insides 28 of the cylinders of the capsules 22 are helically rifled and the outer faces 29 of the centrifugal weights 30 are correspondingly fluted, so that rotation is impartedto the centrifugal weights 30 when they move centripetally and centrifugally in and out in said capsule 22. The fluted outside 29 of each centrifugal weight 30 is connected by spokes 3| to the hub 32 of the weight. The inner 'bores of the hubs 32 are provided with a cross-.sectionally irregular formation, for instance, an internal gear formation which in the manner of'a feather key slidably but non-rotatably guides the weight welded) on the bushing 55,

30 upon the centrifugal or gear shaft 33. Shaft 33 is therefore provided with corresponding irregular formation, e. g. teeth 34.

The hollow shafts 33 have longitudinal clearance slots 35. Through these slots extend the square pins 36, which are countersunk into the ends of the weights 30 and retained upon said ends by cover plates 31. The purpose of the pins 38 will be explained later.

In the outer end of the capsule 22 are seated the rings 38 which in turn accommodate the ball bearings 39. The outer races of said ball bearings, and said rings 38 are fastened in position upon the ends of the capsules 22 by the screw caps 40.

Ball bearing 39 supports the outer end of the centrifugal shaft 33; nut 4| bears endwise upon the inner race of said ball bearing and is held in position upon the centrifugal or gear shaft 33 by cotter 42. The inner, contracted end of centrifugal or gear shafts 33 are supported by ball bearing 43 in hubs 44 extending on opposite sides from the hub l4. Adjacent the inner supported ends the centrifugal or gear shafts 33 show bevel pinion formations 45, into which mesh the bevel gear segments 46. Segments 43 are fastened upon theinner ends of the blades l6 by way of screws 41, and are centralized by pins 48.

By way of the bevel gearing and the pitch of the helical flutes guiding the centrifugal weight 30 in the capsule 22, we establish a straight line ratio between the pitch angle of the blade, and the effective radius of the centrifugal weight. This ratio may be adjusted, so that the torque and centrifugal force are substantially equal at all settings. But in addition we desire to compensate for the slight discrepancy discussed above. This is brought about by weight variations, the means serving this end being described presently:

A clearance recess 49, which accommodates the annulus 50, extends in the hubs 44 around the hub l4. Upon opposite sides the threaded ends of screws 5| are engaged in said annulus and are locked in position by nut 52. The head of each screw 5! is upon the inside of the hollow shaft 33, and rotatably-retaina-by way of a non-friction washer-the cone 53, over which extends the spirally contracted end of the helical tension spring 54. The other end of said spring is threaded onto and is non-rotatedly engaged (e. g.

which is longitudinally stationary and non-rotative in relation to weight 30 and is thus centrifugal shaft 33 by the rectangular pin 36 described above, said pin extending through a suitably broached transverse opening in said bushing.

These springs 55 are substantially at rest and do not exert any tension between bushing 55 and annular ring when the centrifugal weights 30 are in their lowest position, in which they are shown. These springs are gradually extended as the centrifugal weights move apart under centrifugal force and increasingly counteract the centrifugal force; such counteraction deducts from the centrifugal force the amount to which that force exceeds the corresponding torque.

It should be noted that the annulus 50 is shown to be floatingly arranged so that the springs and the reactions may be equalized.

Ordinarily it is neither necessary nor desirable to adjust a variable propeller through all possible pitch positions. In a housing with the limited space of that of Fig. 1, the walls naturally limit positioned in the hollow the movement'of the gear segments. But the propeller expert ordinarily prefers to operate within well defined limits, and for such purposes stops at a high pitch position, as well as at a low pitch may be provided for, as they are shown in later figures.

- In the chart of Fig. 2 the performance of a device of the type .of Fig. 1 is exemplified; on the ordinate we measure torque and reaction. We relate the upper curve, a'straight line which shows the'centrifugal force, to the radius of the center tually attaching weights at preferred points thereof, the centrifugally effective weight center of said level may be shifted in any desired direc- 'tion. If said weight center is above 'the fulcrum 64 for all movement of the gear 63, the centrifugal force will increase less than usual in relation tomovement at the gear circle. But, as suggested above, the fulcrum 64 may be moved. out

- for instance, i. e. away from the axis of the main shaft and close to and even above the center of the effective weight of gear 63, so that the inof gravity on the abscissa. The lower,- torque curve is plotted against-degrees of the pitch angle.

In the arrangement of Fig. 1 the springs 54 are designed to overcome the discrepancy between the two curvees. A blade pitch of 18 relates to a speed of travel of a plane of 175 miles per hour, and roughly that speed changes atthe rate of 1 miles for each 2 degrees of pitch angle."

Fig. 3 illustrates in accordance with item B above, that the discrepancy between torque and centrifugal force may beovercome by changing the path of the centrifugal weight. This arrangement is made under the. presumption that the torque curve may deviate from the centrifu- I g'ear- 63 further out until the propeller blade is gal force curve in fine fashion,-so that the discrepancy in question may beovercome by arranging the centrifugal weightalong a. circular path. 1

In Fig. 3 the housing supports the blade in the same manner as illustrated in Fig. 1. .But the front part 6| of the housing is enlarged and provides a chamber to accommodate the swinging centrifugal weight.v

- While it is ordinarily desirable to compound gearing in order to attain the high ratio of trans- One segment 63 is fulcrumed on the front part 6| of v the propeller housing by a transverse shaft 64.

It should be noted that during .the angular movement of the centrifugal weight, which is directly transmittedby the helical gearing to the blade of the variable propeller, theeffective radius of the centrifugal weight does" not in-' crease in keeping with the circular path of the centrifugal weight around the fulcrum at 64. By

adjustment of the pitch diameter of the gearing segment serving as centrifugal weight, by shifting the center of gravity thereof to a preferred point, and by adjusting the fulcrum in relation to the said center of gravity as well as in relation to the axis of the propeller shaft, the centrifugal reaction may be rendered equal at all times to the torque best adapted for the pitch of the propeller blade, if the discrepancy in question is in the order of a sine function. Other adjustments may be' made by the use of irregular gearing, e. g.

elliptic gearing or byadjusting the pitch of the helical gear segments from point to point.

If, a suggested above, there is a varying gear pitch at the various points of engagement of ears 62 and 63, the pitch diameter of the gears is first chosen to yield the desired movement at an avercrease in centrifugal force becomes larger in relation to movement at the gear pitch circle.-

Thus a fuel compensation between centrifugal force and propeller torque may be obtained leading to the following operation:

Increasing speed of the main shaft will throw adjusted to such asteep angle that the plane moves very fast. and the energy thus consumed prevents a higher speed of the main shaft, or may even reduce the speed of the main shaft.

In the latter case the centrifugal weight collapses towards the axis of the main shaft and reduces the propeller pitch angle. The function is therefore similar to that described'in connection with the other embodiments.

An equivalent of the irregular gearing suggested for the-embodiment of Fig. 3 is used in the illustration of the above-mentioned item C- The remaining figures concern such a modification:

In Figs. 5. and 6 the propeller blades are exemplarily presumed to be 'Journalled in the propeller housing in exactly the same manner as was illustrated in Fig. 1. The gear segment 66' is shown at 65 to be'transversely slidably dovetailed into the bottom end of the propeller blade 16. A pin 48 and screws 41 again locate this gear segment in a preferred position upon the blade,

and the screws 41 are shown to be safeguarded in a tightened position by wire seals 61 which are engaged'upon lugs 68 extendingfrom the inner end of ring 11.

In the modification of Figs. 5 and 6 the gear segment 66 is a doublesegment engaging at opposite ends upon bevel pinions 45' of both centrifugal or gear shafts 33, so that both blades as well as both. centrifugal units are fully interconnected by gearing. This suggests to the experienced designer that the two or more blades of apropeller mayall be balanced in accordance with this invention by a' single centrifugal unit,

although I have shown for purposesof symmetry a centrifugal unit, in connection with each blade of the propellers shown in the drawings.

It is of course also understood, that in accordance with the arrangements of Figs. 5 and 6,

the blades and centrifugal units of Fig. 1 may be positively interconnected by gearing, or that the blades 'of Figs. 5 and 6 may be made independent from'each other by connecting each one to only one centrifugal unit in the manner suggested in Fig. 1, either arrangement having obvious advantages and disadvantages. In like manner, the features of any of the modifications shown in the drawings may be converted for the'other modifications, or the elements of the specific combinationsxof the features may be replaced by equivaage lead of the gear pitch,and the lead of the gears is then adjusted relatively to that starting.

point. By changes in design of gear 63, or by aclent elements known to those acquainted in the mechanical arts.

The capsules 22 of the-centrifugal unit are shown to be arranged in the propeller housing of Figs. 5 and 6-in a manner-similar to that disclosed in connection with the modification of Fig. 1, wire seals 10 being added in order to secure directly in the contracted outer end of the cap sule 22.

The centrifugal weights comprise in this modification a substantially rectangular center lug H rounded off on opposite sides to fit but clear the inside of the capsule; from lug ll extend on opposite sides the hubs 12, this integral assembly being axially slidably, but non-rotatably engaged upon the centrifugal or gear shaft 33, in equivalence to the arrangement of Fig. 1.

But instead of engaging along the full outside by way of a spiral formation upon the fluting upon the inside of the capsules 22, this modification shows stems 14 extending from the opposite rounded sides of the lug ll of the centrifugal weight, said pivots supporting rollers '13 which site sides of the centrifugal weight, I provide a groove or slot 75 upon the inside of a capsule 22, upon opposite sides thereof, in which the said rollers engage, in order to impart rotation to the centrifugal or gear shaft 33. These grooves are shown as slots provided in a cylinder 16, which is suitably fastened upon, for instance shrunk into the capsule 22, whereas the grooves were directly out into the inside of the capsules 22 in the mcdification of Fig. 1.

In the outside of the cylinder 16 I show helical grooves 11, which serve to make this element lighter. These grooves give a bearing in the view of Fig. concerning the exact extent of the slot 15, indicating that the said grooves are not exactly helically disposed, but deviate from a helical path, in order to compensate for the dis-' that the position of the roller 13 in Fig. 5 exemplariiy corresponds substantially to a pitch angle of 14 of the propeller blade, and that at this point the extent of the slot 15 approaches a 45 helix. Extending in both directions from this central position in deviation, from said helix, the slot T5 is adjusted in order to compensate for the discrepancies between the torque and the centrifugal reaction.

While the sectioning of the housing in Fig. 6, and the sections of the part of the centrifugal units there shown, extend substantially in the plane of the propeller axis, I show the propeller housing also sectioned at two points at and near the stop screws 18 (between section lines 8|) in a position set back from the propeller axis substantially to the level of the pitch circumference of segment 66. Thus the stop screws 78 engage suitable formations 19 on one side of the segment, when the segment is in one or the other of its extreme positions. Then the said formations 19 are respectively in the positions 19a and 19b indicated in dot-dash lines in the drawings, which are the maximum and minimum pitch variations permitted, the nut 80 locking the stop screws 18 in preferred position.

The suggestions of the drawings so far described may be readily applied to a propeller with more than two blades. In a symmetrical three-blade arrangement providing a centrifugal unit for each blade according to the modification of Fig. 1 or of the modification of Figs. 5 and 6,

nuts 21-1and the cap 40 in a tightened posi-' tion, and the latter engaging the ball bearing 39 I merely adjust the gearing 46-45 or 66-45 for the new angle of 60 between the axes of the blades and the axes of the centrifugal units.

Such a variable pitch three-blade propeller is shown in the view of Fig. 7. The gears are assumed positively to interconnect all blades and centrifugal units, so that only one stop screw 18 for each of the maximum and minimum positions ofmovement of the blades is shown upon the front part 82 of the propeller housing.

In connection with Figs. 1 and 2 I note a complete balance between the blade torque and the centrifugal reaction at and near a low blade pitch angle of 10, and the helicalfluting on the outside of the weight and'upon the inside of the capsule were there both disposed at As the pitch angle increases, the necessary correction was effected by the increasing counteraction of the spring.

But in plotting the slot 15 of Figs. 4, 5 and 6, I have placed the point at which the effective angle of said slot is exemplarily disposed at 45 at a value of 14 of the blade pitch angle in. which position the centrifugal weight of Fig. 5 is shown. The said effective angle is the helix angle at which the slot 15 guides the roller 13 at the diameter of the centrifugal unit, where rollers I3 engage upon the sides of slots 15. For the data of the chart of Fig. 4 that pitch diameter is 1.875". For a blade torque of 473 inch-pounds at a blade pitch angle of 14, using a ratio of 6:1 between the gears 66 and 45, the torque on the centrifugal or gear shaft is six times smaller than the blade torque and the angular movement of the centrifugal or gear shaft is six times larger, scales for these two values being provided to the extreme right and at the top of the chart of Fig. 4, respectively. For

these conditions a helix angle of 45 is obtained at a blade angle of 14 if a centrifugal weight of .1306 pound is disposed at an effective distance from the axis of the propeller shaft of 3.625,

which is the effective centrifugal radius. The torque curve, i. e. the line marked propeller blade twisting moment and weight reaction in inch pound is then plotted to be parallel with the weight radius line at a blade pitch angle of 14. In coarse steps the following table shows in the first column the blade pitch angle, in a second column the corresponding torque at a preferred propeller speed and normally loading the engine. Next to these figures are evaluated in the third, fourth, fifth and sixth column the torque on the centrifugal or gear shaft, the angles of said shaft based on a zero corresponding to a gear pitch angle of 8, the effective radius of the centrifugal weight, and the helix angle at which the slot 75 guides said weight, respectively:

Blade Blade Torque Gear E ficctive pitch torque. on gear shaft centrifugal angle angle inclrlbs. shaft angle radius 5 0t 75 Inches The helix angle of slot 15 is shown to be separately plotted in the chart of Fig. 4 against the angular positions of the centrifugal .or gear shaft. To the torques plotted against blade pitch angles in Fig. 4' for a particular plane and for a preferred normal speed of its propeller (2400 R. P. M.) also them to novel departures which are developed day by day in the contiguous elements of an aircraft outward movement of the reaction weight would cause the blade pitch angle to increase. On account of the increased pitch the engine labors against a slight overload, and its speed will decrease to 2400 R. P M. Inthe meantime the speed of the aeroplane .has increased again,

further unloading the propeller, so that the speedof the engine again increases;but the blade pitch is correspondingly increased,- and again the propeller speed is pulled back to.2400 R. P. M. This play is repeated time and time again, but the step-up in revolutions per minute is actually not in the quick progress of the aviation industry, it.

' very few revolutions.

would even lead toofar, here to explain all the considerations underlying the various features of the instant invention. A protractor scale is for instance indicated on the conical end face of the bearing extensions l ofthe housing -II at the extreme right of Fig. 1.

It is common practice to provide such a scale either on the stationary heating or on the blade, and a mark on the other one of these-parts allows us to read off the exact angular position of the blade. In combination with such a scale the particular arrangement-of the centrifugal unit facilitates an original setting as well as a resetting for readjustment of the gearinglater; because the capsules 22 may be angularly positioned ad libitum before pins 28 are inserted; and for a quick change of the centrifugal radius relatively fifty, which was used as an example only, but a Third: This continues until the blades reach the maximum angle possible with the engine turning at 2400 R. P. M., or until the blades come tov the pitch angle-as it might be for instance desirable when the propeller is moved from one craft or motor to a different one-it is only necessary to relocate pins 20 in a newangular position of the capsules in the housing.

It is not necessary that the blades and centrifugal units are accommodated in the same plane normal to, the axis of the propeller, the latter might even be placed upon the inside of theformer, co-axially thereto. An allocation of the centrifugal weight to the front of a blade suggests itself.

- The gear segment extending from the blade vmay, instead of by .way of intermediary gearing,

directly engage upon the gear formation on the outside of the centrifugal weight, in which case the weight is preferably non-rotative.

Direct gearing and an arrangement of the centrifugal unit to the front of the blade are illustrated in Fig. 3, except that the modification of Fig. 3 goes further, the weight there being swiveled instead of slidable.

The foregoing description of various modifications of this invention also discloses their operation. But the usefulness of the variable blade propeller of this invention will be betterunderstood from the following exemplary detail consideration of its performance on the basis of various flying conditions and manoeuvers:

First: Assume that the plane is ready to take off. The brakes are locked, but the motor is running at the preferred speed of 2400 R. P. Mr of the propeller shaft. Let us presume that the throttle remains set at this position unless otherwise noted. Under these conditions, while the aeroplane is stationary, the heavy load moves the blade back against the low-pitch stop.

up against the high pitch stops. This. will produce the maximum air speed possible in level flight at the fixed throttle setting, as it is assumed that the ship has now taken off, climbed v to the desired altitude and leveled off.

Fourth: 'At increased altitude an engine with a fixed propeller would increase its propeller speed due to lessened resistance of the thin air; but with my improved propeller, only the blade angle will increase and the engine will maintain at constant speed.

Fifth: Let it now be assumed that the ship is suddenly put into a' steep climb. The engine speed momentarily decreases, reducing the centrifugal force of the reaction weights which move in centripetally, thereby decreasing the angle of the blade pitch so that the engine may immediately pick up speed again, resuming the average level of 2400 R. P. M. at a lower propeller pitch.

Sixth: In a steep dive the action would be the converse of that described in the preceding paragraph. Note that the pitch angle will be much higher at terminal velocity, in case no high pitch stop is provided.

Seventh: For the performance so far described a fixed throttle setting was presumed, yielding an average speed of the engine of 2400 R. P. M. Now let the throttle be pulled back, because it is desired to cruise the ship at a lower propeller speed. The engine speed decreases,

- and analogously to paragraph fifth" the blade Second: Now the brakes are released and the I ship starts to move down the field. This eases the load on the engine, and. the engine attempts to run faster as the ship gains'headway. Let us assume that the speed of the propeller shaft has actually risen to 2450 R. P. M. The rise from 2400 to 2450 R. P. M. would increase the centrifugal force of the reaction weight and the resultant angle is reduced until the blade assumes a fixed setting most favorable in respect to engine speed and horsepower.

Eighth: When the engine is further throttled down for the purpose of landing, its speed again decreases, and the blade angle is correspondingly reduced until the low pitch stop is reached. In

this final position the plane is ready to land or again to take off, or for a quick climb in case of some emergency.

The foregoing description of performance re- I lates to a model in keeping with the chart of Figure 4-, referring to a preferred speed of the engine or propeller shaft of 2400 R. P. M. In connection with the chart of Figure 2 that propeller speed is 2100 R. P. M.

A redesign of the propeller blade and itemsA,

B and C have herein been separately suggested as means for making the blade torque equal to the centrifugal reaction; The use of one of these means does not preclude the simultaneous use of another or of all of the others.-

However it shouldbe borne in mind that simplicity must be the keynote of aeroplane constructionand of this invention '-also, which solves an acute aviation problem in a predominantly practical way, with few elements lending thereby, except as the state of the art and the appended claims may require, for it is obvious that various modifications and changes may be made in the method and form of embodiment of my invention, without departing from the spirit and scope thereof.

What I claim is:

1. In a variable pitch propeller, a housing, a I

propeller blade revolubly mounted in said housing, a centrifugal means, a helix guiding said centrifugal means in said housing outside of said propeller, a gear shaft, reduction gears operatively connecting said shaft to said blade, and means slidably but non-rotatively guiding said gear shaft in said centrifugal means.

2. Ina variable pitch propeller, a housing, a propeller blade revolubly mounted in said housing, a centrifugal means, counteracting means operatively unaffected by centrifugal force and compensating for the discrepancy from a straight line relation between the force exerted in said centrifugal means and the torque of said blade, a helix guiding said centrifugal means in said housing, a gear shaft, reduction gears operatively connecting said shaft with said blade, and means slidably but non-rotatively guiding said gear shaft in said centrifugal means.

3. In a variable pitch propeller, a housing, a propeller blade revolubly mounted in said housing, a centrifugal means alongside of said blade, a tension spring for counteracting said centrifugal means, a helix guiding said centrifugal means in said housing, a gear shaft, reduction gears operatively connecting said shaft to said blade, and means slidably but non-rotatively guiding said gear shaft in said centrifugal means.

4. In a variable pitch propeller, a housing, a propeller blade revolubly mounted in said housing, a centrifugal means, an irregularly curved helix guiding said centrifugal means in said housing, the irregularity of the helix serving to compensate for discrepancy from a straight line relation between the force exerted in said centrifugal means and the torque of said blade, a gear shaft, reducing gears connecting said shaft with said blade, and means slidably but nonrotatively guiding said gear shaft in said centrifugal means. 5. In a variable pitch propeller, a housing, a propeller blade revolubly mounted in said housing, a centrifugal means, a helix of varying pitch guiding said centrifugal means in said housing,

a gear shaft, reducing gears connecting said shaft with said blade, and means slidably but non-rotatively guiding said gear shaft in said centrifugal means, the pitch variations serving to compensate for discrepancy from a straight line relation'between the force exerted by said centrifugal means and the torque of said blade.

6. In a variable pitch propeller, a housing, a propeller blade revolubly mounted in said housing, a centrifugal means, and helical gearing varying in pitch at different points of mesh and operatively connecting said centrifugal means with said blade, the pitch variations serving to compensate for discrepancy from a straight line relation between the force exerted by said centrifugal means and the torque of said blade.

7; In a variable pitch propeller, a housing, a propeller blade revolubly mounted in said housing, a centrifugal means, helical gearing'varying in pitch at different points of mesh and operatively connecting said centrifugal means with said blade, and adjustable stops checking the movement of said gearing in one and in opposite direction, respectively, the pitch variations serving to compensate for discrepancy from a straight line relation between the force exerted by said centrifugal means and the torque of said blade.

8. In combination with the shaft and a pair of relatively angularly spaced and radially disposed revoluble blades of a variable pitch propellerarranged in a plane normal to the shaft, centrifugal weights interposed between said blades in said plane, means guiding said weights normal to the axis of said shaft, and positive gearing operatively connecting said weights with said blades at a linear ratio between the respective movements.

9. In combination with the shaft and a radially disposed revoluble blade of a variable pitch propeller, a centrifugal weight, means guiding said weight normal to the axis of said shaft, a second shaft normal to said propeller shaft and said blade, extending centrally intoand rotated by said weight, and a pair of gears directly connecting said second shaft to said blade.

10. In a variable pitch propeller, a housing, a propeller blade revolubly mounted in said housing, a centrifugal means, and helical gearing varying in pitch at different points of mesh and operatively connecting said centrifugal means at an angle with said blade, the pitch variations serving to compensate for discrepancy from a straight line relation between the force exerted by said centrifugal means and the torque of said blade.

EDWIN H. GODFREY. 

